Doloise Mens Suspenders with 3 Swivel Hooks Belt Loops 1.4 Inch Wide Heavy Duty Adjustable Braces

Do the snaps hook to the belt loops? That's the only way I can see how they would work. Please help me understand.

Can you buy suspender hooks seperately

How to keep suspenders from sliding off shoulders?

Can these be worn under tshirts etc? I really don’t want to be seen wearing suspenders haha